Prospectives for AlN electronics and optoelectronics and the important role of alternative synthesis

Abstract

Future applications for emerging AlN semiconductor electronics and optoelectronics are facilitated by emerging doping technologies enabled by low temperature, non-equilibrium epitaxy. Defect and impurity compensation can be reduced by controlling the surface chemistry with reducing compensating vacancy concentrations being a key driver for lower temperature growth. Contrary to common understanding, low temperature, metal-rich vacuum processes are shown to have higher diffusion lengths than high temperature nitrogen-rich methods. This feature can be utilized to inhibit silicon-DX center formation without compromises in crystal quality. First principles calculations identify the valence split-off band as the dominant hole band contributing to impurity band formation (as opposed to the heavy and light hole bands in other nitrides). This anomalous band structure causes an impurity band to form at dopant concentrations similar to GaN even though AlN has a deeper isolated acceptor energy and results in hole mobilities that are substantially higher than possible in GaN. AlN hole concentrations of ∼4.4 × 1018 cm−3 and 0.045 Ω cm resistivity and electron concentrations of ∼6 × 1018 cm−3 and ∼0.02 Ω cm resistivity are shown and offer substantial promise for future generations of AlN bipolar electronic and optical devices.

AlGaN/AlN Stranski–Krastanov Quantum Dots for Highly Efficient Electron Beam-Pumped Emitters: The Role of Miniaturization and Composition to Attain Far UV-C Emission

“…Under these conditions, the growth kinetics are dominated by Ga, whose diffusion length is larger than that of Al at the QD growth temperature. Under nitrogen-rich conditions, the diffusion energy barrier for Ga adatoms falls within the range of 1.4–1.8 eV, which should lead to diffusion lengths around 2 nm at 720 °C . This theoretical value is in good agreement with a diffusion-limited QD radius around 3 nm, as experimentally observed.…”

“…This theoretical value is in good agreement with a diffusion-limited QD radius around 3 nm, as experimentally observed. In contrast, the mobility of Al is negligible at such a growth temperature, which can have an impact on the geometry and optical performance of QDs with high Al content. – …”

Effect of Extended Defects on AlGaN Quantum Dots for Electron-Pumped Ultraviolet Emitters

“…The shallow pits at the surface of the AlN buffer layer may have been induced by the limited lateral surface mobility of Al adatoms, resulting in the creation of flat terraces and macrosteps. ,, The presence of these steps or shallow pits is favored by the strong strain field in the vicinity of the dislocation, which promotes the emergence of the facets. The approximate angle of 30° between the (0 0 0 1) surface and the exposed facets on the steps indicates that these facets correspond to either {5 −5 0 16} or, most probably, {1 0 −1 3} planes, which are known to have low surface energy. , …”

The Origin of the Yellow Luminescence Band in Be-Doped Bulk GaN

“…A different (as will be shown below) yellow band is observed in GaN doped or implanted with beryllium (Be) [9,[17][18][19]. A renewed interest in doping III-nitrides with Be is fueled by recent findings that shallow Be-related acceptors can potentially be used for conductive p-type GaN and AlN [20][21][22]. We recently studied PL from more than 100 Be-doped GaN samples grown by MOCVD and molecular beam epitaxy (MBE), as well as GaN samples grown by HVPE and implanted with Be or co-implanted with Be and F [23,24].…”